What makes this build innovative?

I have been looking around on mobafire, and I have not seen a Gangplank build with Sheen in it. Why is that? Sheen is the best item for gangplank. It is the key to playing him. Why, you ask?
Because it makes your Parrrley so much better! It doubles your AD when you use Parrrley, so it gives you much more damage.

Pros

Lots of damage

Excellent staying power

Killer, even in early game

Ultimate ulti range

Good heal and cleanse

Cons

Needs a lot of money

Squishy when focused

Doesn't have a good CC

The ulti is very random

Runes

9x Greater Mark of DesolationGreater Mark of Desolation: as proven and explained in Rune tips - what secondary and primary means and more, armor penetration is better than critical chance. In any case, except if you buy Last Whisper, which we don't, because we already have the armor pen. (lolwut..? :P)
9x Greater Seal of Evasion: I think this is the best seal in this case. We don't need HP/lvl and we don't need M/5/lvl, because Sheen gives us enough mana.
9x Greater Glyph of Focus: We have an ulti with a really long cooldown, so this CDr is very nice. Also, I don't think that MR or MR/lvl are superior to CDr in our case.
3x Greater Quintessence of DesolationGreater Quintessence of Desolation: same as for the marks.

Justification:

Sheen - this item is really good on Gangplank throughout the game. It gives us 100% crit chance with Parrrley or after the use of another ability like Raise Morale or Remove Scurvy. Although it does not give a real crit with Parrrley, as the bonus damage is not doubled, it is only 1260g, which is very early in the game, and gives us mana to harass a lot in the laning phase. Also, it's passive stacks with normal crits, which makes us critting double!

I am pretty much insulting you now by thinking you would even consider this when playing Gangplank. I still have to say it, though. You already have a heal, dummy.

Again?

Ok, this is the last time I will insult you. You have a Cleanse under W, just use it properly.

How to play

Laning phase: You can try to get first blood with your laning partner. This will give you 400g (or 200g) very early in the game, and you'll almost be ready to buy Sheen, which is our most important item. You can deal at least 200 damage: 70 with ignite, 80 with Parrrley and about two normal attacks which will deal 2*60 and then your poisondamage. If you're up against a Veigar, you can easily kill him.
If you don't go for first blood, you can still go in the brush often, and shoot the enemy with Parrrley, and get a kill after some harassing. Remember: with the 200 extra mana the Sapphire Crystal gives you, you can harass a LOT.
Don't forget to last-hit minions with Parrrley. It gives you quite a bit of extra gold, and boosts your development.
If you are dominating your lane, play aggresively, but if you do not, hug your turret like it's a huge lasershooting teddy bear. You know, the one you sleep with.

Mid/late game: Try to kill the lizard when you have the time. That buff makes you look like you're some kind of pirate... Wait, what?

Teamfights: Use Raise Morale to make your team do more damage. Also time your Remove Scurvy correctly. For instance: when in the rim of Veigar's cage, or when you get Exhausted.

Ultimate

When in a teamfight, use your ulti in a way that all enemies (might) get hit, and try to aim it a bit to the direction you think the enemies will go. If they are losing, aim your ulti a bit more to the direction of their escape route.

You can also use your ulti to finish off an escaping enemy. Do this by aiming the rim of your ulti at the enemy, with the other end in front of him. That way, they'll have to run through the entire thing.

Conclusion

Thanks a lot for reading this far. I think this guide is the best guide to Gangplank, because it may be the only one that uses Sheen. And as I calculated, Sheen makes your Parrrley a whopping 28% more effective! I think this guide will make you an OP Gangplank. Plank on, everyone.